Semi-quantitative assessment of diffuse hepatic uptake seen in I-131 scans – an indicator of functioning thyroid tissue and disease burden in differentiated thyroid cancer

BACKGROUND: To semi-quantitatively analyze liver uptake of I-131 in diagnostic and post-therapy scans by calculating hepatic to thigh ratios (HTR) and evaluate its clinical significance in management of differentiated thyroid cancer. METHOD: Two hundred forty-nine patients were included in the study. Hepatic to thigh ratio (HTR) of counts were calculated for 249 diagnostic and 104 post-therapy scans. Patients were divided into six study groups based on their disease status:1-Serum thyroglobulin (serum Tg) negative (serum Tg ≤ 4 ng/dl) and scan negative; 2-Thyroid remnant only; 3-Thyroid remnant and lymph node metastasis; 4- Tg positive (serum Tg > 4 ng/dl) and scan negative; 5-Bone or/and lung metastasis, and 6-Only lymph node metastasis. Comparison of HTR between these groups was done using one-way ANOVA test. Correlation of HTR with serum Tg, serum thyroid stimulating hormone (TSH), anti-thyroglobulin antibody (ATg) titer and therapeutic dose of I-131 was also assessed. RESULTS: Comparison of HTR between different study groups (1 to 6) showed significant difference in HTR (p = .001). Study group 5 (bone or/and lung metastasis) showed significantly higher mean HTR compared to other groups (p = 0.001). There was only a weak correlation between serum Tg and HTR (r = 0.395). Dose of I-131 administered also had a weak correlation with HTR (r = 0.207). CONCLUSION: HTR has good correlation with functional status of tumor cells, while it has weak correlation to therapeutic dose of I-131 administered and serum Tg. Increased HTR predicts significant disease burden in the form of distant bone and lung metastasis and may potentially be used as a second prognostic factor apart from serum Tg.